a 4 − z 2 a 2 − 2 z 2 − 1 − z 2 a 2 + 1 a 4 {\displaystyle a^{4}-z^{2}a^{2}-2z^{2}-1-{\frac {z^{2}}{a^{2}}}+{\frac {1}{a^{4}}}}
